In control of a heat source of a fixing unit in an image forming apparatus, there has been a problem of a reduction in overshoot of a surface temperature. The image forming apparatus heats a toner fixing surface to raise the temperature of the toner fixing surface to a target temperature and stops the heating at temperature lower than the target temperature. Such control makes it possible to reduce overshoot of the temperature of the toner fixing surface.
If a narrow sheet is used, there is a portion not in contact with the sheet on the toner fixing surface. In the portion, temperature easily rises in the heating. On the other hand, in a portion in contact with the sheet on the toner fixing surface, temperature less easily rises in the heating. Therefore, the temperature of the entire toner fixing surface sometimes cannot be kept uniform.